由GPS观测结果推导中国大陆现今水平应变场   总被引：45，自引：4，他引：45  

杨国华  李延兴  韩月萍  胡新康  巩曰沐 《地震学报》2002,24(4):337-347

以中国大陆及周边近400个GPS测站的水平运动速率为基础，给出了现今地壳水平应变场结果表明:①中国大陆水平应变为西强东弱，剪应变数值大于正应变数值(绝对值)，应变量级一般为10-8/a，局部区域达到10-7/a，但应变分布不均匀；②南北向应变最突出的部位为中国西南部西段的喜马拉雅条带、西北部的36N~42N段及柴达木断块的北缘；③东西向应变西边缘变化最大．此外，由西向东还具有正负交替的变化特征；④REN(东-北向剪切应变)与Rmax(最大剪切应变)数值较大的区域分别是喜马拉雅条带、西北部的36N～42N段、柴达木断块的西部、川滇菱形块体，以及阿拉善、祁连及塔里木断块的交界区；⑤青藏块体周边以面收缩为主，内部则以面膨胀为主．其以北的地区以面收缩为主．西界数值最大，东部数值最小(除燕山构造带外)；⑥西部西区主压应变为南北向，主张应变为东西向．西部东缘区主压应变为近东西向，主张应变为近南北向．川滇菱形块体主应变的方向发生了很大的变化，北部地区为东西压南北张，南部地区则恰好相反；⑦中国大陆的应变模式可能是断块模式与连续模式的组合．此外，小尺度优势应变可能是剪切应变．造成上述结果除与印度板块的碰撞及边界耦合有关外，还与深部物质的活动及地壳介质的物性有密切的关系．必须指出，由于GPS测站在空间上分布的不均匀性，那么，由此而来的应变场，其应变尺度也不一样．   相似文献   

Study of weathering processes developed on old piedmont surfaces in Western Spain: new contributions to the interpretation of the “Raña” profiles     

E. Molina Ballesteros  M. Cantano Martín   《Geomorphology》2002,42(3-4)

The Hercynian basement of the Iberian Peninsula was uplifted by the Alpine orogeny during the Tertiary. It gave rise to a set of block mountains and tectonic grabens, one of which is the Ciudad Rodrigo Basin. It is located in Western Spain and forms a westward extension of the great Tertiary Duero Basin. The sediments filling this graben are of continental origin, their ages ranging from Palaeogene to Quaternary. Morphologically, the southern part of this basin forms a set of piedmont surfaces (the “Raña” surfaces) appearing above the terrace system of the present rivers. This paper examines the weathering processes developed over these old piedmont surfaces using micromorphological, XR diffraction, scanning electron microscopy (SEM) and microporosity techniques.The Raña sediments are rich in quartzite pebbles and gravel within a clayey matrix. Once deposited, these materials underwent important in situ weathering processes under somewhat hydromorphic conditions, of which hydrolysis, ferrolysis and xerolysis were the most important. All these processes gave rise to: (1) transformation of most of the clasts of shists and slates into a matrix causing the destruction of the original sedimentary structures and a relative concentration of the resistant lithologies (quartzites and quartz); (2) important changes in the clay fraction, leading to a predominance of kaolinite in the upper levels of the profiles, (3) release of elements from primary minerals, Fe being one of the most important, and (4) redistribution of matter, mainly clay and Fe oxyhydroxides, within the profiles.The coexistence of seasonal periods with pF higher than 4.2 repeated over a long time, together with poor internal and external drainage conditions, are the cause of the special features displayed by Raña deposits.  相似文献   

Use of Noise to Augment Training Data: A Neural Network Method of Mineral–Potential Mapping in Regions of Limited Known Deposit Examples     

Warick M. Brown  Tamás D. Gedeon  David I. Groves 《Natural Resources Research》2003,12(2):141-152

One of the main factors that affects the performance of MLP neural networks trained using the backpropagation algorithm in mineral-potential mapping isthe paucity of deposit relative to barren training patterns. To overcome this problem, random noise is added to the original training patterns in order to create additional synthetic deposit training data. Experiments on the effect of the number of deposits available for training in the Kalgoorlie Terrane orogenic gold province show that both the classification performance of a trained network and the quality of the resultant prospectivity map increasesignificantly with increased numbers of deposit patterns. Experiments are conducted to determine the optimum amount of noise using both uniform and normally distributed random noise. Through the addition of noise to the original deposit training data, the number of deposit training patterns is increased from approximately 50 to 1000. The percentage of correct classifications significantly improves for the independent test set as well as for deposit patterns in the test set. For example, using ±40% uniform random noise, the test-set classification performance increases from 67.9% and 68.0% to 72.8% and 77.1% (for test-set overall and test-set deposit patterns, respectively). Indices for the quality of the resultant prospectivity map, (i.e. D/A, D × (D/A), where D is the percentage of deposits and A is the percentage of the total area for the highest prospectivity map-class, and area under an ROC curve) also increase from 8.2, 105, 0.79 to 17.9, 226, 0.87, respectively. Increasing the size of the training-stop data set results in a further increase in classification performance to 73.5%, 77.4%, 14.7, 296, 0.87 for test-set overall and test-set deposit patterns, D/A, D × (D/A), and area under the ROC curve, respectively.  相似文献   

Use of Fuzzy Membership Input Layers to Combine Subjective Geological Knowledge and Empirical Data in a Neural Network Method for Mineral-Potential Mapping   总被引：3，自引：0，他引：3  

Brown  Warick  Groves  David  Gedeon  Tamás 《Natural Resources Research》2003,12(3):183-200

Use of GIS layers, in which the cell values represent fuzzy membership variables, is an effective method of combining subjective geological knowledge with empirical data in a neural network approach to mineral-prospectivity mapping. In this study, multilayer perceptron (MLP), neural networks are used to combine up to 17 regional exploration variables to predict the potential for orogenic gold deposits in the form of prospectivity maps in the Archean Kalgoorlie Terrane of Western Australia. Two types of fuzzy membership layers are used. In the first type of layer, the statistical relationships between known gold deposits and variables in the GIS thematic layer are used to determine fuzzy membership values. For example, GIS layers depicting solid geology and rock-type combinations of categorical data at the nearest lithological boundary for each cell are converted to fuzzy membership layers representing favorable lithologies and favorable lithological boundaries, respectively. This type of fuzzy-membership input is a useful alternative to the 1-of-N coding used for categorical inputs, particularly if there are a large number of classes. Rheological contrast at lithological boundaries is modeled using a second type of fuzzy membership layer, in which the assignment of fuzzy membership value, although based on geological field data, is subjective. The methods used here could be applied to a large range of subjective data (e.g., favorability of tectonic environment, host stratigraphy, or reactivation along major faults) currently used in regional exploration programs, but which normally would not be included as inputs in an empirical neural network approach.  相似文献   

贵州雷公山背斜南段锑矿控矿条件浅析     

范玉梅 《贵州地质》2003,20(4):216-219,215

本文根据雷公山背斜南段的几个锑矿床的勘查资料，结合1：5万区调和相应的科研成果，总结该区锑矿床的共同特征，并对其控矿条件进行分析，认为逆冲断层、剪切带控制锑矿田的分布，“褶皱 断层”控制锑矿床分布，单条剪切带及后期脆性断层控制锑矿体的产出。  相似文献   

斑岩铜矿中铂族元素的研究现状及展望   总被引：4，自引：0，他引：4  

李晓峰  毛景文  张作衡 《矿床地质》2003,22(1):95-98

文章对当前国内外斑岩铜矿中铂族元素的研究现状进行了较为详细的阐述，指出研究与铂族元素矿化有关的斑岩铜矿的流体包裹体及其富集成矿过程，以及铂族元素对斑岩铜矿成矿环境，成岩岩浆的起源和成矿物质来源示踪是该领域的发展方向和前沿。  相似文献   

蒙甘新相邻(北山)地区金铜矿床时空分布特征及成矿作用   总被引：14，自引：1，他引：14       下载免费PDF全文

聂凤军  江思宏  白大明  刘妍  张义  赵月明  安存杰  王新亮  苏新旭 《矿床地质》2003,22(3):234-245

文章首次对蒙甘新相邻(北山)地区各类金、铜和铜—镍矿床(点)地质特征、成因类型和空间分布特点进行了系统总结，论证了金、铜和铜—镍成矿作用与古生代岩浆活动的关系，对区域地壳演化过程中金、铜和铜—镍成矿的动力学机制进行了深入讨论。研究结果表明，该区的金矿床(点)大体可划分为变质岩型、火山岩型、斑岩型和深成侵入岩型；铜矿床(点)有斑岩型、夕卡岩型和铜—镍硫化物型。金和铜矿床(点)大都沿古板块汇聚带分布，与海西期火成岩具密切的时空分布关系，它们是古板块对接碰撞期和碰撞期后大规模构造—岩浆活动的产物。  相似文献   

浅谈研究和寻找超大型矿床的理论和方法   总被引：1，自引：0，他引：1  

燕长海  刘国印  宋峰 《矿产与地质》2003,17(3):203-206

寻找大型矿床是一项十分，艮巨、复杂、综合性极强的工作^[1]。研究和寻找大型—超大型矿床的理论和方法可分为：①大型—超大型矿床的成矿条件和成矿模式(巨量矿质、流体和能量的有利匹配和稳定供给，成矿系统的矿源场、中介场和储矿场的结构集约化，适时的成矿启动，稳定持续的成矿作用和成矿后的良好保存)；②地质分析法(构造环境分析、地质建造分析和地质构造分析)；③勘查地球物理方法；④勘查地球化学方法；⑤遥感地质方法。  相似文献   

我国钴矿矿产资源及其成矿作用   总被引：10，自引：0，他引：10  

潘彤 《矿产与地质》2003,17(4):516-518

钴广泛应用于军事、钢铁、电器、机械等方面，它具有亲铁亲硫的双重性，在各类岩浆岩中的分布不均匀，由超基性岩向酸性岩，钴的含量迅速降低。我国钻矿资源呈现富矿少、贫矿多的特点，并且铬矿主要分布在甘肃、青海、新疆、吉林、陕西、云南、四川等地。按照矿床形成的成矿环境、矿床岩石组合，矿床类型划分为：与镁铁质-超镁铁质岩有关的硫化物钻矿、与海相火山喷发有关的钻多金属矿、与斑岩有关的铜钻矿、与砂岩有关的钻矿、与中酸性侵入岩有关的矽卡岩铁钻矿、与风化作用有关的钴矿等六类。  相似文献   

李坝式金矿床成矿作用及矿床类型探讨   总被引：5，自引：2，他引：5  

程彧  卢哲  张东旭  田继孝 《矿产与地质》2003,17(5):594-597

李坝式金矿床成矿作用过程分为成矿元素初始富集期和构造叠加热液改造成矿期，岩浆活动主号是通过改变矿床地质体物化条件而促进矿化体的形成，并有部分岩浆物质参与成矿。该矿床与国内外经典卡林型金矿床具有较大的可比性，但是由于缺乏低温矿物组合以及与岩浆活动的亲密性证据，该矿床应属广义上的卡林型金矿床。  相似文献